The present invention relates to a modular fuel tank and mounting arrangement for a vehicle such as a truck or a bus and a method of installing same on the vehicle. More specifically, the design of the mounting arrangement allows the fuel tank and entry/egress steps to be sub-assembled off of a main assembly line and brought to the main assembly line as a unit for installation with little or no alignment required. The mounting arrangement may be applied to other modular assemblies for vehicles such as battery boxes and air tanks.